Black-and-white developers for silver halide photographic materials generally contain dihydroxybenzenes (particularly, hydroquinone), 3-pyrazolidones, alkaline agents and sulfites as basic constituents.
It is common knowledge in the art that when photographic materials are to be processed in an automatic processor of the type generally used in recent years in the development of radiographic silver halide photographic materials, a dialdehyde-type hardener is added in order to reinforce the mechanical strength of the emulsion film of the photographic materials. Details of the are described, for example, in U.S. Pat No. Re. 26,601, U.S. Pat. No. 3,545,971, and British Pat. No. 1,269,268. It is well known in the art, as also described in the specifications of the above-cited patents, that since the use of dialdehyde-type hardeners in developers causes inherently high fogging by these compounds, it is absolutely necessary to add organic antifoggants which specifically inhibit this fogging, for example, indazole-type compounds, benzotriazole-type compounds, benzimidazole-type compounds, anthraquinonesulfonic acid-type compounds, mercaptotetrazole-type compounds and thiadiazole-type compounds.
Many organic antifoggants which specifically inhibit the fogging caused of the dialdehyde-type hardeners are known, and examples include
5-nitroindazole, PA1 5-p-nitrobenzoylaminoindazole, PA1 1-methyl-5-nitroindazole, PA1 6-nitroindazole, PA1 3-methyl-5-nitroindazole, PA1 5-nitrobenzimidazole, PA1 2-isopropyl-5-nitrobenzimidazole, PA1 5-nitrobenzotriazole, PA1 2-thiazolylmethylbenzimidazole, PA1 hydroxyazaindolidine, PA1 1-phenyl-5-mercaptotetrazole, PA1 2-mercaptobenzothiazole, PA1 thiosalicyclic acid, PA1 benzothiazole, PA1 sodium 1-anthraquinonesulfonate, PA1 sodium 2-anthraquinonesulfonate, PA1 thiazole, PA1 1-(N,N-diethylamino)ethylmercaptotetrazole, PA1 sodium 4-(2-mercapto-1,3,4-thiadiazol-2-yl-thio)butanesulfonate, PA1 5-amino-1,3,4-thiadiazole-2-thiol, PA1 2-(2,4-dinitrophenylmercapto)benzothiazole, and PA1 3-ethyl-5-o-nitrobenzylidene-1-phenyl-2-thiohydantoin.
It is the general practice nowadays to subject a radiographic silver halide photographic material to a rapid processing treatment in an automatic processor, e.g., for 3.5 minutes or 90 seconds, and a so-called PQ developer comprising a combination of hydroquinone and 3-pyrazolidone-type developing agents is frequently used in order to increase developing activity.
In the development of silver halide photographic materials, calcium ions often get into the developer. It is considered to be derived from water used and from the silver halide/gelatin emulsion. Calcium ions react with carbonates and sulfites in the developer to form a precipitate of calcium carbonate and calcium sulfite. Such a precipitate is undesirable because it causes the formation of a sludge in the developer solution, a scum on the photographic material and a deposit on the developer tank.
Attention has long been paid to a method of remedying the undesirable development caused by such precipitates, and attempts have been made to prevent the formation of such precipitates by using compounds which can convert the calcium ion in the developer solution into the form of a soluble complex.
Alkali metal salts of hexametaphosphoric acid, and polyphosphoric acid salts such as alkali metal salts of tetraphosphoric acid are compounds which are characteristic in the above sense. These compounds are known to prevent precipitation of calcium salts in the developer. However, these compounds tend to undergo hydrolysis to orthophosphoric acid in the developer. Orthophosphoric acid no longer has the property of hiding the calcium ion, and rather becomes a cause of formation of calcium phosphate. When an orthophosphoric acid salt is carried into a fixing bath containing aluminum ions, such as an ordinary acidic hardening-fixing bath, aluminum phosphate may be undesirably precipitated.
Organic acids such as citric acid, tartaric acid and gluconic acid have the ability of a calcium masking agent, but in most cases, have a lower masking power than polyphosphates.
Compounds such as ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) have long been known, and have proved to be satisfactory in respect of stability in developers and a masking effect. However, if a trace of an iron or copper salt exists together in the developer, such a compound forms an iron chelate compound or a copper chelate compound which acts catalytically to undesirably promote the air oxidation (autoxidation) of the hydroquinone developing agent. For example, when EDTA is added to a developer containing several ppm of iron, the air oxidation of the developing agent occurs at a speed more than 3 times as fast as that at which it occurs in the absence of EDTA. At the same time, in the presence of EDTA, the pH of the developer increases and adversely affects the stability of the developer with time.
The applicability of other various chelating agents to black-and-white developers (for example, the PQ developer) for general silver halide photographic materials is described in L. F. A. Mason, Photographic Processing Chemistry (1975, Focal Press, London), or Research Disclosure RD Nos. 18837 (December, 1979) and 20405 (April, 1981).
Thus, although many compounds have been suggested as a calcium masking agent for use in photographic processing liquids, they have only weak efficacy or secondary defects and are not entirely satisfactory. Even EDTA now is widespread use has the aforesaid serious defect. If this defect could be overcome, the developing operation would be able to be performed continously over long periods of time with good stability and high quality.